safari basic authentication

our non profit orginization needs to be able to pass authentication through safari browser as we do not want to put an app in the app store because its just for our members only we also would not want to charge for the app we also do not want to pay for a developer account to have to sideload an app for hundreds of devices and them expire we dont have the time we also do not have a mac but we dont have problems with android users just iphone users which makes up about 95 percent of our members so we have decided the best solution for us is for our members to just save a web widget to there phones that accesses our mobile app like site this is also great because we do not have to worry about physical contact with a pc or mac to sideload an app or updates on each device as everything is just handled on our server but we want to restrict all access to our internal network by having to supply basic authentication for prohibited individuals but at the same time allow those who need access to access it from the outside without having to supply authentication every single time as they have already been authenticated through there profile where the web widget url resides it also doesnt make good for an app like experience we also cannot setup htaccess for every ip address as phones ip addresses change on cellular networks the address bar has been removed from the web widget url using html code when accessing it so noone can visually see the actual url and authentication credentials its fullscreen and once they are no longer a member there profile accounts become disabled by management we also do not want to make everyone create a registered account just to access the app link as we have guest with seperate apps different from member apps but we need http://loginusernamehere:passwordhere@domain.compasswordhere@domain.com to pass through safari any thoughts or suggestions